Week 8 - July 1-5

Introduction

Videos

Quiz

• Quiz 6 will be on sockets. Please study from Sockets Tutorial. A more advanced tutorial can be found at C++ Tutorial: Sockets - Server and Client.

Lecture Material

• Sockets: Introduction - Chapter 56 of The Linux Programming Interface.
• Sockets: Unix Domain - Chapter 57 of The Linux Programming Interface.
• Sockets: Internet Domains - Chapter 59 of The Linux Programming Interface.
• Sockets: Server Design - Chapter 60 of The Linux Programming Interface.
• A Simple Makefile Tutorial
• Sockets Tutorial.
• C++ Tutorial: Sockets - Server and Client.
• Another tutorial with TCP sockets Introduction to Sockets Programming.
• Another tutorial with UDP sockets Programming with UDP sockets.

Lab

• Lab 6 - server/client communications.

Assignment(s)

Assignment 1.

Sample Code

Makefiles, continued

• Alternative forms of Makefile - see A Simple Makefile Tutorial.
  See also Makefile1, Makefile2, Makefile3, and Makefile4 and the source code for hellomake.c, hellofunc.c and hellomake.h.
  Makefile5 assumes three directories which are next to each other on a file system: a src directory, an obj directory and an include directory.
  The Makefile, hellomake.c, hellofunc.c are in the src directory. The file hellomake.h is in the include directory, and all object files are in the obj directory.
  After make clean all, du -a would give:
  4 ./include/hellomake.h
  4 ./include
  4 ./obj/hellofunc.o
  4 ./obj/hellomake.o
  8 ./obj
  4 ./src/hellofunc.c
  12 ./src/hellomake
  4 ./src/hellomake.c
  4 ./src/Makefile
  24 ./src
  36 .

Sockets

• Please take note of the different socket domains.

  Domain	Communication	Communication	Address	Address
  AF_UNIX	performed	between applications	format	structure
  	within kernel	on same host	pathname	sockaddr_un
  AF_INET	via IPv4	on hosts connected	32-bit IPv4 address +	sockaddr_in
  		via an IPv4 network	16-bit port number
  AF_INET6	via IPv6	on hosts connected	128-bit IPv6 address +	sockaddr_in6
  		via an IPv6 network	16-bit port number

• Every sockets implementation provides at least two types of sockets: stream and datagram. These socket types are supported in both the UNIX and the Internet domains.
  Stream sockets (SOCK_STREAM) provide a reliable, bidirectional, byte-stream communication channel.
  Datagram sockets (SOCK_DGRAM) allow data to be exchanged in the form of messages called datagrams. With datagram sockets, message boundaries are preserved, but data transmission is not reliable. Messages may arrive out of order, be duplicated, or not arrive at all.
• When using IP addresses and IP ports for socket communications, keep in mind the list of commonly used port numbers.
  To get a list of ports that are free on a Linux machine, use the command line argument netstat or ss. For example:
  $ netstat -lntup
  $ ss -lntup
  -l listening sockets,
  -n numeric values rather than service names,
  -t all TCP connections,
  -u all UDP connections,
  -p application that is listening on a port.
  For more information on netstat, see also 10 basic examples of linux netstat command,
• Another tutorial with TCP sockets can be found at Introduction to Sockets Programming, and
  a tutorial with UDP sockets can be found at Programming with UDP sockets.
• For a discussion on UDP vs TCP, see the article UDP vs TCP: What are they and how do they differ?.
• For common socket function calls see socket(), bind(), listen(), connect(), accept(), select()/FD_SET()/FD_ISSET(), inet_pton(), inet_ntop(), read(), write(), send()/sendto(), recv()/recvfrom(), getsockopt()/setsockopt(), close(), and unlink().
• A simple client server application demonstrating UNIX type sockets can be found in client1.cpp, server.cpp, and Makefile.
  
• A simple client server application demonstrating INET type sockets can be found in client.c, server.c, and Makefile. This code also demonstrates INADDR_ANY. When INADDR_ANY is specified in the bind() call, the socket will be bound to all local interfaces.
  
• A simple client server application demonstrating inter-process communication between processes on two different machines can be found in msgClient.cpp, msgServer.cpp, and Makefile.
  For this to work, msgClient has to be on one machine and msgServer on another. This means you have to create another virtual linux machine, run msgServer on one and run msgClient on the other. Be sure to use the address of the machine that runs msgServer. This example also introduces setsockopt() to set the socket with a timeout of 5 seconds.
• An example with select (a server with 5 clients) can be seen at Select5.docx.
  The source code for the server can be found at server.cpp, and the source code for the clients can be found at client.cpp
  A shell to start the clients can be found at startClient.sh, and the Makefile can be found at Makefile.